Paleoproterozoic metaluminous syenites synchronous with the c. 2.21 Ga mafic dyke swarms from the Eastern Dharwar Craton, India: implications for alkaline magmatism associated with the breakup of supercraton Superia

AbstractThe Eastern Dharwar Craton (EDC) hosts numerous Late Neoarchean to Paleoproterozoic syenites whose genesis remains unclear. Here we present a petrological and geochemical study on the syenites from Peddavaduguru, Danduvaripalle and Vannedoddi, towards the western margin of the Paleo-Mesoproterozoic Cuddapah Basin in the EDC. These syenite bodies constitute a part of the Paleoproterozoic (2210 ± 110 Ma) Dancherla alkaline complex and are contemporaneous with a mafic dyke swarm emplacement in the EDC. The Danduvaripalle and Vannedoddi syenites display geochemical affinities to adakites. The Peddavaduguru syenite shows a negative Eu anomaly and relatively gentle chondrite-normalized rare earth element (REE) pattern, suggesting an origin by a different process. The ɛNd values range between 0.5 and 0.8 for the Peddavaduguru syenite, − 5.2 and − 4.2 for the Danduvaripalle syenite, and − 6.0 and − 1.0 for the Vannedoddi syenite. In tectonic discrimination diagrams, the Peddavaduguru syenite shows affinities to within-plate granitoids similar to syenites from the Deccan large igneous province whereas the others show geochemical similarities to arc-related alkaline rocks and volcanic arc granitoids. The adakitic syenites show deficiency of MgO, Ni, Cr and Sc, highly fractionated REE patterns and negative Nb–Ta–Ti anomalies along with low Nb/U and high Th/U ratios. These geochemical traits are compatible with their origin by the partial melting of a mafic crustal source that subsequently underwent fractionation of amphibole and garnet responsible to impart an adakitic character. We suggest that the crustal source of these syenites underwent partial melting by heat from the rising plume during the Paleoproterozoic extension of the Superia supercraton. The non-adakitic Peddavaduguru syenite, on the other hand, is suggested to have originated from direct fractionation of mafic magma.